The present invention relates to a power converter device such as an inverter device for driving a motor at a variable speed, an uninterruptible power supply unit, or the like.
FIG. 11 is a view showing a configuration of an inverter device as a power converter device according to the related art.
In FIG. 11, reference numeral 30 is an AC power supply, reference numeral 31 is an inverter device, reference numeral 32 is a converter portion for converting the AC power into the DC power, and reference numeral 33 is a capacitor for smoothing the DC voltage. Also, reference numeral 34 is an inverter portion for inverting the DC power into the AC power that has the variable frequency and the variable voltage, the inverter portion having output power elements, which has self turnoff elements (referred to as xe2x80x9cswitching elementsxe2x80x9d hereinafter) Tr1, Tr2, Tr3, Tr4, Tr5, Tr6 and free wheeling diodes D1, D2, D3, D4, D5, D6. Also, Vuo is a potential of a connection point u between the switching elements Tr1 and Tr2, Vv0 is a potential of a connection point v between the switching elements Tr3 and Tr4, and Vw0 is a potential of a connection point w between the switching elements Tr5 and Tr6.
Also, reference numeral 35 is a control portion for ON/OFF-controlling the switching elements of the inverter portion 34, and reference numeral 36 is a motor such as the induction motor that is driven at a variable speed as a load.
Also, reference numeral 40 is a CPU as an arithmetic circuit for receiving various commands such as an operation command, a speed command, etc. and various set values such as an accelerating/decelerating time, a V/f pattern, etc. as input signals, calculating an output frequency and an output voltage, and outputting switching signals Su1, Su2, Sv1, Sv2, Sw1, Sw2 to turn the switching elements ON/OFF. Also, reference numeral 41 is a memory as a storing means for storing various data such as the accelerating/decelerating times, a relational expression between the output frequency/output voltage, etc.
Also, reference numeral 42a to 42f are driving portions for amplifying the switching signals Su1, Su2, Sv1, Sv2, Sw1, Sw2, which are output from the control portion 35, up to base signals having amplitudes that can drive the switching elements Tr1, Tr2, Tr3, Tr4, Tr5, Tr6.
As this output voltage controlling system, there are the pulse width modulation (abbreviated to xe2x80x9cPWMxe2x80x9d hereinafter) and the pulse amplitude modulation (abbreviate to xe2x80x9cPAMxe2x80x9d hereinafter). With reference to the example of the PWM system that the output voltage is controlled by changing time periods during which the switching elements Tr1, Tr2, Tr3, Tr4, Tr5, Tr6 of the inverter portion 34 are turned ON, explanation will be described hereinafter.
The CPU 40 receives various commands (not shown) such as the operation command, the speed command, etc. and various set values such as the accelerating/decelerating time, the V/f pattern, etc. stored in the memory 41 as the input signals, calculates the output frequency and the output voltage, and outputs the switching signals Su1, Su2, Sv1, Sv2, Sw1, Sw2 to turn the switching elements ON/OFF.
FIG. 12 is a view showing various waveforms of the inverter device in the PWM system according to the related art, wherein (a) is a view showing relationships between command voltage waveforms Vur, Vvr, Vwr in a U phase, a V phase, a W phase and a carrier wave Vtri, (b) is a view showing a command voltage waveform Vu at a connection point u between the switching elements Tr1 Tr2, (c) is a view showing a command voltage waveform Vv at a connection point v between the switching elements Tr3 and Tr4, (d) is a view showing a command voltage waveform Vw at a connection point w between the switching elements Tr5 and Tr6, and (e) is a view showing an inverter output voltage waveform Vuv=Vuxe2x88x92Vv.
The CPU 40 compares the command voltage waveforms Vur, Vvr, Vwr shown in (a) with the carrier wave Vtri, and then brings the switching elements into their ON state if the command voltage waveforms are larger than the carrier wave, and brings the switching elements into their OFF state if the command voltage waveforms are smaller than the carrier wave, as shown in (b), (c), (d).
Next, an operation of the inverter device according to the related art will be explained hereunder.
When the power supply is turned ON, the converter portion 32 converts the AC power of the AC power supply 30 into the DC power and smoothes this DC power by the capacitor 33.
Also, the control portion 35 receives various commands such as the operation command, the speed command, etc. and various set values such as the accelerating/decelerating time, the V/f pattern, etc. as the input signals, calculates the output frequency and the output voltage, and outputs the switching signals Su1, Su2, Sv1, Sv2, Sw1, Sw2 to turn the switching elements ON/OFF.
Also, the inverter portion 34 converts the DC power into the AC power having the variable frequency and the variable voltage by ON/OFF-controlling the switching elements Tr1, Tr2, Tr3, Tr4, Tr5, Tr6 based on the switching signals Su1, Su2, Sv1, Sv2, Sw1, Sw2 output from the control portion 35.
The AC power having the variable frequency and the variable voltage is supplied to the motor 36, whereby this motor 36 can be driven at a variable speed.
FIG. 13 is a view showing output voltages of the inverter device according to the related art, wherein (a) is a view showing the voltage waveform Vu0 at the connection point u, (b) is a view showing the voltage waveform Vv0 at the connection point v, (c) is a view showing the voltage waveform Vw0 at the connection point w, and (d) is a view showing the voltage waveform of the output voltage Vuv0 (=Vu0xe2x88x92Vv0).
In FIG. 13, E is a command voltage, Vuo is a potential waveform of the connection point u between the switching elements Tr1 and Tr2, Vv0 is a potential waveform of the connection point v between the switching elements Tr3 and Tr4, Vw0 is a potential waveform of the connection point w between the switching elements Tr5 and Tr6, and VTr1_ON, VTr2_ON, VTr3_ON, VTr4_ON, VTr5_ON, VTr6_ON are saturation voltages, respectively when the switching elements (Tr1, Tr2, Tr3, Tr4, Tr5, Tr6) are turned ON.
As shown in FIG. 13, in the ON/OFF control of the switching elements (Tr1, Tr2, Tr3, Tr4, Tr5, Tr6), the saturation voltages (VTr1_ON, VTr2_ON, VTr3_ON, VTr4_ON, VTr5_ON, VTr6_ON) are present when the switching elements (Tr1, Tr2, Tr3, Tr4, Tr5, Tr6) are turned ON. Therefore, the potential Vu0 at the connection point u has an amplitude of E-VTr1_ONxcx9cVTr2_ON as shown in (a), the potential Vv0 at the connection point v has an amplitude of E-VTr3_ON VTr4_ON as shown in (b), and the potential Vw0 at the connection point w has an amplitude of E-VTr5_ONxcx9cVTr6_ON as shown in (c).
For this reason, the output voltage Vuv0 when the switching elements Tr1, Tr4 are turned ON is given as not Vuv0=Exe2x88x920=E, but                     Vuv0        =                  (                      Vu0            -            Vv0                    )                                        =                              (                          E              -              VTr1_ON                        )                    -          VTr4_ON                                        =                  E          -                                    (                              VTr1_ON                +                VTr4_ON                            )                        .                              
In contrast, the output voltage Vuv0 (=Vu0xe2x88x92Vv0) when the switching elements Tr2, Tr3 are turned ON is given as not Vuv0=0xe2x88x92E=xe2x88x92E, but                     Vuv0        =                  (                      Vu0            -            Vv0                    )                                        =                  VTr2_ON          -                      (                          E              -              VTr3_ON                        )                                                  =                              (                          VTr2_ON              +              VTr3_ON                        )                    -                      E            .                              
In the inverter device according to the related art, the command voltage is supplied to the inverter as the input voltage as it is. Therefore, the amplitude of the output voltage does not have the amplitude of the command voltage Excx9cxe2x88x92E, but the amplitude of the actual output voltage is in the range of
Exe2x88x92(VTr1xe2x80x94ON+VTr4xe2x80x94ON)xcx9cE+(VTr2xe2x80x94ON+VTr3xe2x80x94ON), 
whereby the part of the saturation voltages becomes the error.
It is possible to get the smooth output, in which the low order harmonics contained in the output voltage of the inverter is reduced by the PWM system. However, the command voltage is supplied to the inverter as the input voltage as it is, and thus the saturation voltages of the switching elements in the inverter operation are not taken into consideration. Therefore, in the inverter operation, the inverter output voltage for generating the saturation voltage of the switching elements does not coincide with the voltage indicated by the command value, and thus there is the problem that the precise voltage cannot be output.
Also, there is the system that the actual output voltage is measured such that the inverter output voltage coincides with the value indicated by the command, and then the voltage that is subjected to the saturation voltage compensation is input into the inverter. But this system needs to add the circuit separately, and thus there are the problems that a cost is increased and a size of the circuit is increased.
In addition, the input voltage of the motor is low in the low-speed operation range, and the influence of the saturation voltage of the switching elements is enhanced relatively. Thus, there is the problem that the speed ripple in the low-speed operation range is increased.
The present invention has been made to overcome above such subjects, and it is a first object of the present invention to provide a variable-speed control apparatus that is capable of estimating saturation voltages of switching elements in the inverter operation to execute a saturation voltage compensation and thus getting an inverter output voltage indicated by a command value.
Also, it is a second object of the present invention to provide a variable-speed control apparatus that is capable of estimating easily the saturation voltages of switching elements in the inverter operation.
A power converter device of the present invention has an inverter portion having a switching element and a free wheeling diode element, the inverter portion for converting a DC power into an AC power, a control portion for ON/OFF-controlling the switching elements of the inverter portion, and a current sensor for sensing current flowing through one of the switching element and the free wheeling diode element, in which the control portion has a current discriminating circuit for discriminating that sensed currents sensed by the current sensors are either current flowing through the switching elements or current flowing through the free wheeling diode elements, a saturation voltage estimation table for showing relationships between temperature of the switching element, current value of the switching element, temperature of the free wheeling element, and current value of the free wheeling element and saturation voltages of the switching elements; and a saturation voltage compensating unit for receiving the temperature of the switching element and the current discriminated by the current discriminating circuit, estimating a saturation voltage of the switching element by using the saturation voltage estimation table, and forming saturation voltage compensated voltage in which a command voltage to an inverter is compensated with the estimated saturation voltage, and in which the switching elements of the inverter portion are ON/OFF-controlled based on the saturation voltage compensated voltage. Therefore, the reduction in the inverter output voltage due to the saturation voltage of the switching element can be prevented and thus the more precise voltage control can be achieved.
A power converter device of the invention has an inverter portion having a switching element and a free wheeling diode element, the inverter portion for converting a DC power into an AC power, a control portion for ON/OFF-controlling the switching elements of the inverter portion, and a gate voltage detecting circuit insulating circuit for detecting gate voltage of the switching element, in which the control portion has a current discriminating circuit for discriminating that sensed currents sensed by the current sensors are either current flowing through the switching elements or current flowing through the free wheeling diode elements, a saturation voltage estimation table for showing relationships between temperature of the switching element, current value of the switching element, temperature of the free wheeling element, and current value of the free wheeling element and saturation voltages of the switching elements, and a saturation voltage compensating unit for receiving the gate voltage of the switching element and the current discriminated by the current discriminating circuit, estimating a saturation voltage of the switching element by using the saturation voltage estimation table, and forming saturation voltage compensated voltage in which a command voltage to an inverter is compensated with the estimated saturation voltage, and in which the switching elements of the inverter portion are ON/OFF-controlled based on the saturation voltage compensated voltage. Therefore, even if the load is heavy and the saturation voltage is changed depending on the magnitude of the gate-emitter voltage in the ON-state of the switching elements, the saturation voltage can be compensated with good precision and thus the more precise voltage control can be achieved.
In addition, temperature sensors are fitted to the switching element and the free wheeling diode element to sense temperature of the switching element and temperature of the free wheeling diode element. Therefore, the temperatures of the switching elements and the free wheeling diode elements can be sensed precisely.
Also, temperature sensor is fitted in the vicinity of the switching element and the free wheeling diode element, which constitute a pair, on a substrate on which the switching element and the free wheeling diode element are mounted. The control portion estimates temperature of the switching element and temperature of the free wheeling diode element based on substrate temperature sensed by the temperature sensor, stationary thermal resistance between the switching element and the substrate, stationary thermal resistances between the free wheeling diode element and the substrate, heating value of the switching element calculated based on the sensed current, and heating value of the free wheeling diode element calculated based on the sensed current. Therefore, the fitting of the temperature sensors can be facilitated.
In addition, a temperature sensor is fitted to one location on a substrate on which the switching element and the free wheeling diode element are mounted. The control portion estimates temperature of the switching element and temperature of the free wheeling diode element based on substrate temperature sensed by the temperature sensor, stationary thermal resistance between the switching element and the substrate, stationary thermal resistances between the free wheeling diode element and the substrate, heating value of the switching element calculated based on the sensed current, and heating value of the free wheeling diode element calculated based on the sensed current. Therefore, the fitting of the temperature sensors can be made much more easy.
Further, temperature sensors are fitted to a location on a fin fitted to a substrate on which the switching element and the free wheeling diode element are mounted, the location corresponding to the switching element and the free wheeling diode element. The control portion estimates temperature of the switching element and the free wheeling diode element based on substrate temperature sensed by the temperature sensors, stationary thermal resistance between the switching element and the substrate, stationary thermal resistance between the fin and the substrate, stationary thermal resistance between the free wheeling diode element and the substrate, the stationary thermal resistance between the fin-the substrate and heating values of the switching element calculated based on the sensed currents, and heating values of the free wheeling diode element. Therefore, the fitting of the temperature sensors can be further facilitated.
Furthermore, temperature sensor are fitted to a location on a fin fitted to a substrate on which the switching element and the free wheeling diode element are mounted, the location corresponding to a pair of the switching element and the free wheeling diode element. The control portion estimates temperature of the switching element and temperature of the free wheeling diode element based on substrate temperature sensed by the temperature sensor, stationary thermal resistances between the switching element and the substrate, a stationary thermal resistance between the fin and the substrate, stationary thermal resistances between the free wheeling diode element and the substrate, the stationary thermal resistance between the fin and the substrate, heating value of the switching element calculated based on the sensed current, and heating value of the free wheeling diode element calculated based on the sensed current. Therefore, the fitting of the temperature sensors can be made easy further more.
Besides, temperature sensor is fitted to one location on a fin that is fitted to a substrate on which the switching element and the free wheeling diode element are mounted. The control portion estimates temperature of the switching element and temperature of the free wheeling diode element based on substrate temperature sensed by the temperature, stationary thermal resistances between the switching element and the substrate, stationary thermal resistance between the fin and the substrate, stationary thermal resistances between the free wheeling diode element and the substrate, stationary thermal resistance between the fin and the substrate, heating value of the switching element calculated based on the sensed current, and heating value of the free wheeling diode element based on the sensed current.